1. Field of the Invention
The present invention relates to a field emission display (FED) and especially, to an FED device.
2. Description of the Background Art
Recently, with the development in the telecommunication techniques, demands on displays are increasing and structures of displays are varied. For instance, in environment requesting mobility such as mobile type information appliances, a light, small display with smaller power consumption is favored, while a display is used as a general information transfer medium, it needs to have a large screen such as a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), a VFD (Vacuum Fluorescent Display).
Accordingly, developments of a compact FED that can have high resolution but reduced power consumption are actively ongoing.
The FED receives an attention as a next-generation telecommunication flat display, because it overcomes shortcomings of flat displays (e.g., the LCD, the PDP and the VFD) which are under development or mass-produced.
The FED device has lots of merits as a display device in that it has a simple electrode structure, operates at high speed under the same principle as the CRT and has an infinite color, infinite gray scale and high luminance.
FIG. 1 is a sectional view showing the structure of a general field emission display device.
As shown in FIG. 1, the FED device includes a lower glass substrate 1; a cathode electrode 2 formed on the lower glass substrate 1; an emitter 5 and an insulator layer 3 formed at a portion of the cathode electrode 2; a gate electrode 4 formed on the insulator layer 3; an upper glass substrate 9; an anode electrode 8 formed on the upper glass substrate 9 and applying a high voltage so that electron beams can be generated from the emitter 5; a phosphor layer 7 excited by electron beams emitted from the emitter 5 by the high voltage to emit visible rays; and a spacer 6 disposed between the gate electrode and the anode electrode 8 in order to support the upper glass substrate 9 and the lower glass substrate 1.
The emitter 5 is formed in a micro tip shape and has excellent electron emission characteristics, but in order to fabricate a display device with a large screen of 20 inches or wider, a large-scale equipment are required and its fabrication processes are complicate.
A conventional surface conduction type FED device has a simple structure and commonly used for a large-screen display device.
The construction of the surface conduction type FED device will now be described with reference to FIG. 2.
FIG. 2 is a sectional view showing the structure of the surface conduction type FED device in accordance with a conventional art.
As shown in FIG. 2, the surface conduction type FED device includes: a lower glass substrate 17; a gate electrode 16 and a cathode electrode 14 formed on the lower glass substrate 17; a first emitter 15-1 formed on a portion of the cathode electrode 14; a second emitter 15-2 formed on a portion of the gate electrode 16; an upper glass substrate 11; an anode electrode 12 formed on the upper glass substrate 11 and applying a high voltage; and a phosphor layer 13 formed on the anode electrode 12 and emitting visible lights by being excited by electron beams generated by the first and second emitters 15-1 and 15-2 by the high voltage.
A narrow gap 18 is formed between the first and second emitters 15-1 and 1502. When a threshold voltage is applied to the gate electrode 16 and the cathode electrode 14 formed at the lower portion of the first and second emitters 15-1 and 15-2, high electric field is generated at the gap 18, by which electrons are emitted.
The electrons emitted by the first and second emitters 15-1 and 15-2 are accelerate by the high voltage applied to the anode electrode 12 and converted into electron beams, which is then converged on the phosphor layer 13. Then, the phosphor layer 13 is excited by the electron beams to emit visible rays. Herein, the first and second emitters 15-1 and 15-2, the gate electrode 16 and the cathode electrode 14 are called a single field emission device.
A matrix structure of the surface conduction type FED device employing the FED will now be described with reference to FIG. 3.
FIG. 3 illustrates an example of a matrix structure in accordance with the surface conduction type FED device in accordance with the conventional art.
As shown in FIG. 3, the surface conduction type FED device includes: a plurality of scan lines Scan 1˜Scan N; a plurality of data lines D1˜Dm 30 crossing the plurality of scan lines Scan 1˜Scan N; and FED devices formed at the crossings of the scan lines (e.g., Scan 1) and data lines (e.g., D1).
A field emission device of the FED device is installed at each of a red pixel, a green pixel and a blue pixel. The gate electrode 16 of the field emission device is electrically connected to the data line (e.g., D1) and the cathode electrode 14 of the field emission device is electrically connected to the scan line (e.g., Scan 1).
For example, in the matrix structure of the surface conduction type FED, when a threshold voltage is applied to the first scan line Scan 1 and the first data line D1, a field emission device electrically connected to the first scan line (Scan 1) and the data line (D1) emits electron beams and the electron beams excite a fluorescent material (e.g., a red fluorescent material). At this time, an area 100 of electron beams emitted from one field emission device is smaller than an area of the phosphor layer 13. Namely, since the electron beams emitted from one field emission device is smaller than the area of the phosphor layer 13, the overall area of the phosphor layer 13 cannot be excited.
The area of the electron beams converged on the phosphor layer 13 will be described with reference to FIG. 4 as follows.
FIG. 4 illustrates the area of electron beams emitted from the field emission device of the surface conduction FED device in accordance with the conventional art.
As shown in FIG. 4, the electrons are emitted in the direction of the anode electrode due to a tunneling effect by the first and second emitters 15-1 and 15-2 of the field emission device. Thus, electrons emitted by the first and second emitters 15-1 and 15-2 are bent in the direction of the gate electrode and accelerated in the direction of the anode electrode 12. Electrons (electron beams) accelerated in the direction of the anode electrode excite only a portion of the phosphor layer 13, causing a problem of degradation of luminance and efficiency of the surface.
Thus, as mentioned above, the conventional surface conduction type FED device is disadvantageous that since the electron beams emitted from the field emission device excites only a portion of the phosphor layer, luminance and efficiency of the surface conduction type FED device deteriorate.
The conventional field emission device and the techniques for the FED device are also disclosed in U.S. Pat. Nos. 6,169,372 and 6,646,282.